Along with the development of mobile communication technologies, more and more new technologies, such as Multi-User Multiple Input Multiple Output (MU-MIMO), heterogeneous network (HetNet) and New Carrier Type (NCT), are introduced into a communication system so as to improve the performance thereof, and these technologies rely heavily on Physical Downlink Control Channel (PDCCH). The wide application of these technologies will lead to a shortage of PDCCH capacity. In order to solve this problem, Enhanced Physical Downlink Control Channel (ePDCCH) is introduced so as to expand the PDCCH capacity.
FIG. 1 shows a basic framework of ePDCCH. An ePDCCH domain and Physical Downlink Shared Channel (PDSCH) are multiplexed in frequency division multiplexing manner to support interference coordination. A base station configures the resource for ePDCCH domain via RRC signaling. In addition, ePDCCH performs data demodulation based on DM-RS, so it can obtain a gain via beam-forming. For ePDCCH, it is one of the core designs to design a search space in the ePDCCH domain.
For PDCCH, all users in a cell will monitor an identical control domain. Blind detection is performed by each user in the control domain so as to determine whether or not there is PDCCH transmitted from the base station to the user in the control domain. Search space is introduced so as to reduce the times of blind detection at a user end. Briefly, search space is a series of potential PDCCH positions, the number of which depends on the size of control information, as shown in FIG. 2. The base station and the user allocate the search space resources according to a Hashing function.
For ePDCCH, because it occupies the PDSCH resources, not only a traditional index, e.g., collision probability, but also a resource utilization efficiency shall be taken into consideration when performing the corresponding search space design.
Recently, several search space designs have been presented. The most direct and simplest way is to perform search space allocation with a Hashing function in all the ePDCCH domains configured by the base station. However, a shortcoming of such way is that the resource utilization efficiency is relatively low when there are few users. In order to improve the resource utilization efficiency, a method of dynamically informing the resources is presented. In this method, the base station tries at first to perform the search space allocation with a Hashing function in a part of the configured resources, tries again to perform the search space allocation in more resources if there is an ePDCCH collision, until no ePDCCH collision occurs or all the configured resources have been used up. Then, the base station will inform the user of the resources actually used via dynamic information (via ePCFICH), and the remaining configured resources may be multiplexed as PDSCH so as to improve the resource utilization efficiency, as shown in FIG. 3.
However, such a search space allocation mode is still inflexible, and the resource utilization efficiency is still low. For example, as shown in FIG. 4, the method of the prior art tries at first to perform the search space allocation in the resources corresponding to “00”, then in the resources corresponding to “01” if there is an ePDCCH collision, and then in the resources corresponding to “10” if there is still the ePDCCH collision. As a result, the resources corresponding to “01”, other than the resources corresponding to “00”, will be wasted. In addition, actually only a part of the resources corresponding to “10”, other than those corresponding to “01”, is allocated for transmitting user control information, and the others will be wasted too.